Photoluminescence Enhancement in Thin Two-Dimensional Ruddlesden-Popper Perovskites by Spiro-OMeTAD

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskite materials have been widely studied as optoelectronic and photonic devices because of the combination of advantages of perovskites and the unique excitonic properties in the 2D limit. However, thin 2D perovskite flakes, in general, suffer from a weak photoluminescence (PL) emission because of surface defects related to nonradiative recombinations. Here, we demonstrate that the PL of thin 2D RP perovskites can be enhanced by the introduction of spiro-OMeTAD, which effectively passivates the surface defects of RP perovskites. By steady-state and time-resolved PL spectroscopy, we investigate the interaction between spiro-OMeTAD and RP perovskite flakes with different thicknesses and find that along with the enhanced PL intensity, the PL lifetime is prolonged, which agrees with the reduction in nonradiative recombination. In contrast, for thicker perovskite flakes, the spiro-OMeTAD leads to PL quenching and a shortened PL lifetime, due to the reduced surface effect and the formation of a type-II band alignment with the perovskites. Our research provides an effective method to enhance the PL emission of thin 2D RP perovskites, which could promote the future device applications of RP perovskites.